1. Field of the Invention
The present invention relates to an image forming apparatus that can be used for an electrophotographic copying machine or a printer.
2. Description of the Related Art
The development of the highly computerized society in recent years has entailed the current popularity of copying machines and printers that are being used not only in offices but also in ordinary homes. At the same time, the trend of down-sizing such apparatus is advancing. Meanwhile, various mobile equipments like color television sets, color displays of personal computers and game machines available these days have been rapidly developed to provide color images. Similarly, colorization of electrophotographic copying machines and printers is remarkably advancing. To reflect the development of various colorized mobile equipments and their popularity, many book stores, convenience stores and other stores currently have color copying machines and color printers that are publicly accessible and hence people can use them for the purpose of copying various documents and leaflets they want even if they are away from the office or the home.
Particularly, the popularity of digital still cameras is remarkable in these days. This is mainly because the user can shoot a scene while monitoring the picked up image of the scene and replay the recorded image and also because the user can transmit the obtained image by way of a communication network. There seem to be many people who want to obtain hard copies of the picture taken by a digital still camera by means of a color printer.
Existing electrophotographic printers and copying machines for black and white images are mostly adapted to produce less glossy images by regulating the fixing temperature and the fixing time of toner because it is rather difficult to read letters printed on glossy paper. While electrophotographic printers and copying machines for producing color images such as graphics and diagrams have become available recently, they essentially employ a mechanism similar to its counterpart for black and white images so that the user may be able to regulate the fixing temperature and the fixing time of toners by selecting a desired processing speed.
However, it is preferred to want to have hard copies of pictures taken by digital still cameras that are as glossy as photographs. Therefore, electrophotographic printers and copying machines for producing glossy images need to use a mechanism basically different from the one for producing black and white images and/or color images such as graphics.
There have been proposed image forming apparatus provided with an annexed unit for outputting highly smooth and highly glossy images in addition to a conventional unit (see, inter alia, Patent Document 1).
FIG. 1 of the accompanying drawings is a schematic view of such an image forming apparatus provided with an annexed unit for outputting highly smooth and highly glossy images in addition to a conventional unit.
The image forming apparatus shown in FIG. 1 has a main body section 101 and an annexed unit 150 containing a belt fixing device, paper feed roll and so on.
The main body section 101 has an image processing section 104 for converting red (R), green (G) and blue (B) colors of the image data readout from an image reading section (not shown) or externally input into yellow (Y), magenta (M), cyan (C) and black (K) colors, a sensitized body 107 adapted to rotate in the sense of arrow A in FIG. 1 to form a toner image, a charger 108 for uniformly charging the sensitized body 107 with electricity, an exposure section 105 for irradiating light modulated according to the image data of Y, M, C and K colors output from the image processing section 104 to the sensitized body 107 that has been electrically charged to form electrostatic images of Y, M, C and K colors, a rotary developing device 109 for containing toners 109Y, 109M, 109C and 109K of different colors fed respectively from toner boxes 135 of Y, M, C and K colors and developing the electrostatic latent images of Y, M, C and K colors on the sensitized body 107 by means of toner of the respective colors to form toner images of Y, M, C and K colors on the sensitized body 107 and a cleaner 132 for cleaning out the residual toner after transferring the toner images.
The main body section 101 further has an intermediate transfer belt 111 held by a drive roll 113, a tension rolls 114 and an opposite roll 115 and driven to move around in the direction of arrow B in FIG. 1 while being held in contact with the sensitized body 107, a primary transfer roll 112 that forms a nip section with the sensitized body 107 with the intermediate transfer belt 111 held between them and is adapted to transfer toner images on the sensitized body 107 to the intermediate transfer belt 111 and a secondary transfer roll 117 that forms another nip section with the opposite roll 115 with the intermediate transfer belt 111 held between them and is adapted to secondarily transfer the toner images on the intermediate transfer belt 111 to a sheet of paper P.
The main body section 101 additionally has a sheet tray 118 containing sheets of paper P to be used for forming images thereon, a conveyance route 120 along which each sheet of paper P drawn out of the sheet tray 118 is conveyed to the secondary transfer position where a toner image is transferred onto it, a conveyance belt 121 for conveying the sheet of paper P carrying toner images to a fixing position and a roll fixing device 125 for fixing the toner images on the sheet of paper P by nipping it between a pair of rolls 122, 123 and applying heat and pressure to it.
The sensitized body 107 that is uniformly charged with electricity by the charger 108 is exposed by the exposure section 105 to light modulated according to the image data of Y, M, C and K colors to form electrostatic latent images thereon, which are then developed by the developing device 109 to produce toner images of Y, M, C and K colors. The toner images of Y, M, C and K colors are then sequentially transferred to the circulating intermediate transfer belt 111 one on the other by the primary transfer roll 112 so that a toner image of Y, M, C and K colors is formed on the intermediate transfer belt 111 by superposition. The multicolored toner image is then secondarily transferred to the sheet of paper P by the secondary transfer roll 117 and fixed to the sheet of paper P by the roll fixing device 125.
The image forming operation is terminated here in the case of forming an image of ordinary image quality. Then, a conveyance route switch 152 is turned to the side of a discharge roll 154 and the sheet of paper P carrying the image fixed by the roll fixing device 125 is delivered to a discharge section 155 of the annexed unit 150 by way of the discharge roll 154.
In the case of forming a highly glossy photographic image, on the other hand, a sheet of coat paper having a surface layer of thermoplastic resin that operates as an image receiving layer is fed either from a dedicated tray (not shown) or from a tray 134 where a number of sheets of coat paper have been manually stored. Subsequently, as a result of passing through the steps described above for an image of ordinary image quality, a multicolored toner image is secondarily transferred onto the sheet of coat paper and the image formed by the superposition is fixed by the roll fixing device 125. Then, the conveyance route switch 152 is turned to the side of the conveyance rolls 157 and the sheet of coat paper is fed to a belt fixing device 158 in the annexed unit 150 by way of the conveyance rolls 157. The belt fixing device 158 has an endless belt that runs and is held by a roll having a heat source in the inside. Thus, as the surface of the sheet of coat paper P that carries the fixed toner image is laid on the endless belt, the fixed toner image on the sheet of paper P is gradually heated again and smoothed. Then, the heater toner image is cooled by a cooling member (not shown) and solidified to become a highly glossy image.
Thus, a belt fixing device 158 is used in order to provide a long fixing time when forming an image of photographic image quality. The belt fixing device 158 requires a relatively large space if compared with a roll fixing device for producing an image of ordinary image quality. Therefore, an image forming apparatus adapted to produce a highly glossy image has dimensions that are twice as large as an apparatus for producing only an ordinary image if such an annexed unit is used.
There is also an image forming apparatus provided with a belt fixing device in addition to a conventional roll fixing device, in which the two fixing devices are arranged in series. In this apparatus, the sheet of paper to which toner images have been transferred is driven to pass either of the two fixing devices or both of them. If it is made to pass through the two fixing devices, a glossy image, a semi-glossy image or a non-glossy image can be obtained by changing the order in which the sheet of paper is made to pass through the fixing devices (see, inter alia, Patent Document 2).
[Patent Document 1]
Japanese Patent Publication No. 4-31393 (Page 2, FIG. 1)
[Patent Document 2]
Japanese Patent Application No. 5-1583864 (Paragraph No. 0007 through Paragraph No. 0014, Paragraph No. 0018 through Paragraph No. 0031, FIGS. 2 through 4).
However, an image forming apparatus as disclosed in Patent Document 1 contains a unit for forming a highly smooth and glossy image that is arranged in juxtaposition with the unit for forming an ordinary image and therefore, it requires internal space for containing two units. Also, two fixing devices of different types are arranged horizontally in series in an image forming apparatus as disclosed in Patent Document 2, and therefore, the entire image forming apparatus has large dimensions so that, once again, it requires large internal space if compared with conventional apparatus.
While various information-related apparatus have been down-sized in recent years, the number of installed apparatus has been increasing. This means that a newly designed apparatus that requires a larger space for installation than a comparable conventional apparatus may not have an appreciable commercial value and will not sell well. Particularly, an image forming apparatus that is produced by technological innovations is required to have dimensions comparable to those of a conventional image forming apparatus if it is installed in a limited space in a book store, a convenience store or the like.